A comparison of hemispatial neglect from posterior parietal and periarcuate lesions in the monkey

In this experiment, we examined hemispatial neglect in the monkey, comparing unilateral parietal lesions with lesions of frontal cortex. Our purpose was to resolve the apparent puzzle of grave parietal symptoms in humans shown only inconsistently in monkeys. We quantitatively compared visual neglect and recovery in monkeys with unilateral posterior parietal, periarcuate, and principal sulcus (control) lesions. Neocortical lesions of these three regions were produced in 9 macaque monkeys, and they were tested for their ability to detect and respond to brief visual stimuli in varying field eccentricities. Both parietal and arcuate lesions resulted in neglect. Recovery from the arcuate lesion occurred by the 3rd postoperative week, but neglect was strongly evident in the parietal animals in the 8th week. A second homologous lesion produced a more severe and enduring neglect of contralateral stimuli and also reinstated neglect in the hemifield affected by the first lesion. These data confirm symptoms of visual neglect from parietal lesions and are consistent with differentiated functions of posterior parietal and arcuate cortex in spatial attention.